Cylindrical grinding worms are used for the continuous generation grinding of gear wheels. Because the grinding worm is subjected to natural wear and tear during this process, it has to be dressed from time to time, i.e., the material is removed from the flanks of the thread or the threads of the grinding worm with the dressing tool and the external diameter of the worm is also redressed corresponding to the amount of the radial advance in the dressing of the flanks.
A method of the type described above is known from DE 102 20 513 A1 (corresponding to US 2004/005843). With the known method, a grinding worm can be dressed in the tangential as well as in the diagonal process. In both cases, the gear wheel dressing tool performs a rectilinear move relative to the grinding worm. The relative movement occurs on a plane that is defined by the rotational axis of the dressing tool and by a parallel to the rotational axis of the grinding worm. FIG. 3 of the attached drawings describes the parallel to the rotational axis of the grinding worm as Y-axis, and the rotational axis of the gear wheel dressing tool, which is arranged relative to the Y-axis under the so-called crossed-axes angle, is described as the Z-axis.
During the machining in the tangential process, the relative movement 19 of the dressing tool is performed tangentially to the grinding worm, i.e., parallel to the Y-axis. During machining in the diagonal process, the rectilinear relative movement 20 of the dressing tool has a component in the direction Z. Because only a small part of the width of the dressing tool is used during the machining in the tangential or diagonal process, the wear and tear across the width of the dressing tool, i.e. in axial direction, is irregular. If the dressing tool operating in the tangential process is worn in a specific area of its width, it can be shifted in its axial direction to use the parts of the tool width that were not used previously. Because the tooth profile is not always exactly uniform across the width of the dressing tool for production reasons, the shift of the dressing tool may result in variations in the profile quality of the grinding worms dressed with the various areas of the dressing tool width. However, the deviations in the profile are reproduced in the gear wheels that are then ground with the grinding worms.
During the machining in the diagonal process, different areas of the width of the dressing tool engage with the grinding worm. For the reasons mentioned above, it is therefore difficult to obtain a grinding worm with a uniform profile across the entire width. This problem apparently increases with the width of the grinding worm. To extend the service life of the grinding worm, it is known to develop the grinding worm in a length that is many times longer than the engagement width used during the grinding. This creates the opportunity to shift the grinding worm in axial direction to bring an area that is not worn into engagement with the gear wheel to be ground. However, because the profile of a grinding worm dressed in the diagonal process is usually not uniform across the width of the grinding worm, for the reasons explained above, the gear wheels ground with the varying axial areas of the grinding worm are also not uniform. In a repeated dressing of the grinding worm in the tangential or in the diagonal process, it can therefore not be guaranteed that quality of the profile of the end product, i.e. the gear wheels, is uniform, regardless of what width area of the grinding worm was used in their grinding or how often the grinding worm was dressed.
The object to be attained by the invention is to modify the generic method so that the profile of the dressed grinding worms remains uniform across the width, and that the profile of each dressed worm is uniform across the useable width of the worm.